Behringer KX1200 Keyboard Amp Speaker Wiring Question

[DrGonz78]

So I just finished repairing this amp so that part is good. Someone had cut the speaker out wiring from the amp that connects to the crossover board so I had to disconnect the Piezo tweeter from circuit and now I am not sure which way to wire it back in the cab. The amp has a 3 way crossover system with woofer wired black wire(ground) goes to negative and blue wire goes to positive. Then the mid range speaker connects black(ground) to the positive terminal and white to the negative terminal. So to me that indicates that the woofer and mid range speakers are wired up in series. Then the mid range speaker is wired directly to the piezo speaker. So now would I wire up the piezo tweeter in parallel or series of the mid range speaker? Also, note that I measure about 500k resistance across the piezo tweeter and I am not sure if the peizo is still good. Also, note that all the other wiring has been undisturbed and is the way that it was originally. I just can remember how the piezo connects together. Thanks for any thoughts on this one.

[Richard]

Piezo tweeters are commonly just connected in parallel with a speaker. A piezo acts like a capacitor and blocks low frequencies and impedance of speakers usually rises at higher frequencies so a crossover is not strictly needed. Maybe Behringer does something different but grounds are usually tied together and each crossover has a high and low output, the high output may go to another crossover to split off the highs from the mids.

[DrGonz78]

Thanks for the info . I am now curious about this crossover so I drew it up on schematic layout to view it better. Very simple but I am curious if other members might want to help me understand it better. I am confused by phase of signal and polarity of the wiring of the different speakers. How are the speakers in phase with each other?

[mozwell]

Doctor, That looks about right to me
The behringer K3000FX has the woofer connect direct to the power amp, & the tweeter connect to the power amp with a PTC & 2u2 in series with the tweeter positive

Connect it all up & run it, you wont hurt anything

[Jazz P Bass]

Not at all uncommon for the tweeter to be out of phase.

Edit: here is the K3000 X Over that Moz mentioned.

behringer_k3000fx_X Over.pdf

[J M Fahey]

Thanks for the info . I am now curious about this crossover so I drew it up on schematic layout to view it better. Very simple but I am curious if other members might want to help me understand it better. I am confused by phase of signal and polarity of the wiring of the different speakers. How are the speakers in phase with each other?

1) all 3 speakers are connected basically in parallel (all have one leg to grond) , and the free legs are connected through some crossover element, not direct.

2) the woofer is connected as expected: - leg to ground, + leg to hot but through an inductor, which stops mids and highs. Fine

3) the midrange also has one leg connected directly to ground, but we have a problem: the woofer has a series inductor which changes phase by 90 degrees at the crossover frequency, midrange has a series capacitor which also changes phase 90 degrees ... the opposite way
Net results:
a) now audio is equally reproduced by woofer and midrange at the same time, 50/50 split between them so they are putting out the same ... but both audio waves are 180 degrees out of phase.
b) so they add destructively and you have a *deep* notch at the crossover frequency.
Practical solution?: you invert one of them, the least damage is done by inverting the midrange.

Is that an elegant solution?
No, quite kludgy/crude ... but it works, so .......

4) the tweeter has also a capacitor in series, behaves similar to midrange, phase is shifted similar to midrange, it is also connected out of phase with woofer.
Personally I don't much agree and prefer to reverse phase again with midrange, but don't want to start a war.

Pssssttttt Juan !!!! **which** tweeter capacitor???? I see not one in the schematic.
Oh, that? ...the Piezo element **is** a capacitor (in fact I measured them between .082 and .15uF ) and of course behaves as such.

M

[DrGonz78]

Thanks everyone for all the great advice and information. I have yet to really work on much where I even dealt with a crossover so this has been an eye opener. Juan your explanation was excellent!! I had been wondering if the piezo was not working and if it was removed how that might effect the crossover circuit. Now I see that in this example that the piezo plays two roles.